Method for treatment of spent hydrochloric acid pickle liquor for the recovery of iron oxide, ammonium sulphate and hydrochloric acid



June 10, 1958 c. D. STRICKER 2,338,373

METHOD FOR TREATMENT OF SPENT HYDROCHLORIC ACID PICKLE LIQUOR FOR THERECOVERY OF IRON OXIDE, AMMONIUM SULPHATE AND HYDROCHLORIC ACID FiledMay 2a, 1956 CHARIL E5 0. STRICKER, ADJ-144 540 & Am

his Attorney United States Patent METHOD FOR TREATMENT OF SPENT HYDRO-CHLORIC ACID PICKLE LIQUOR FOR THE RE- COVERY OF IRON OXIDE, AMMONIUMSUL- PHATE AND HYDROCHLORIC ACID Charles D. Stricker, Shaker'Heights,Ohio, assignor to United States Steel Corporation, a corporation of NewJersey Application May 23, 1956, Serial No. 586,810

2 Claims. (Cl. 23-119) This invention relates to the treatment of spentpickle liquor and, in particular, to the treatment of hydrochloricacidliquor in such manner as to recover hydrochloric acid and iron oxide.

This is a continuation-in-part of my application Serial 7 No. 489,135,filed February 18, 1955.

Hydrochloric acid is used extensively as a pickling agent in the steelindustry. It is more expensive than sulphuric acid, the other commonpickling agent, but the latter is not satisfactory for all picklingoperations. The disposal of spent liquor, whether hydrochloric-acid orsulphuric-acid, remains a. serious problem, despitemany previousproposals for the treatment thereof.

I have invented a process for treating spent hydrochloric-acid liquor soas to recover all the solute in readily usable form, i. e., as ironoxide and hydrochloric acid. Briefly, my process includes-treating thespent liquor with ammonia and oxygen to precipitate iron oxide and leavea solution of ammonium chloride. I then react the chloride solution withammonium bisulphate to produce a mixed solution of ammonium sulphate andhydrochloric acid. From this solution, I boil off the hydrogen chlorideand crystallize the ammonium sulphate. The hydrogen chloride vapor, whencondensed, is available for use in making up fresh pickle liquor and theammonium sulphate may be decomposed by heat into ammonia and ammoniumbisulphate for use in treating more spent liquor.

A complete understanding of the invention may be obtained from thefollowing detailed description thereof with reference to theaccompanying drawing which is a diagrammatic representation of theseveral apparatus units involved in a continuous treating systemutilizing the invention.

Referring now in detail to the drawing, a pickling tank 1 contains thewaste liquor to be treated. The liquor, of course is a solution offerrous chloride and hydrochloric acid in water. A suitable volume ofliquor is pumped from tank 1 to a reactionchamber 2 where gaseousammonia and air are bubbled therethrough from sources 3 and 4,respectively. The ammonia must be supplied in suflicient amount toneutralize the acid and convert the ferrous chloride to ammoniumchloride, and the air in sufficient amount that the oxygen thereofoxidizes the ferrous ions to iron oxide which is precipitated fromsolution. The details of a practice suitable for use at this stage aregiven in Hoak Patent No. 2,529,- 874, dated November 14, 1950. By addingproper amounts of air along with the ammonia, much of the ferrous ironis converted to ferric. By the correct proportioning of the reactantsand air, rapid settling ferrosoferric hydrated oxide is formed, withcomplete precipita-,

tion of iron at pH 7.5 to 8.0. The ferric to ferrous ratio should bekept between 2:1 to 3.5 :1.

The slurry resulting from the ammoniation and oxidation is pumped fromchamber 2 through a heater 5 by pump 6 to 'a continuous filter 7. Theheater raises the temperature of the slurry to a pointat which theammonium chloride is fully dissolved. This depends on the concentrationof the chloride in slurry. Filter 7 separates the precipitated ironoxide from the ammonium chloride solution. The oxide is collected in anysuitable container, such as a vehicle 8, for removal. It is inimmediately usable form for purposes such as sinter feed. A settlingtank may be used for separation instead of the filter 7.

The ammonium chloride flows to a reactor 9 heated by steam to atemperature between and 124 C. Ammonium bisulphate is suppliedcontinuously to chamber 9 through a connection 10, at the same molarrate as the chloride. The chamber has bafiles 11 therein to effectthorough mixing. The reactions in chamber 9 are:

The hot solution passes from chamber 9 to a crystallizer 12 where it isconcentrated by evaporation. Aslurry of ammonium sulphate crystalsformed in crystallizer 12 is delivered to a continuous vacuum filter 13which separates the crystals at 14 and returns solution to thecrystallizer. Hydrogen chloride and water vapor boiled oil from thesolution leave the crystallizer through a connection 15. The vapors arecondensed in cooling coils .16 and collect as pure hydrochloric acid ina container 17, from which the acid may be returned to the pickling tankfor making up a fresh batch of liquor.

Solid ammonium sulphate from ,filter 13 is delivere to a dissociationchamber 18 heated to a temperature between 250 and 400 C. At thattemperature, the sulphate decomposes into ammonia and ammoniumbisulphate. The bisulphate is collected in a container 19 and isavailable for use in treating further amounts of ammonium chloride inchamber 9. Ammonia gas leaving chamber 18 is available for similar usein chamber 2.

It will be apparent from the foregoing that the invention provides asimple and effective method for the treatment of spent hydrochloric-acidpickle liquor, having several important advantages. In the first place,it results in no by-products requiring disposal since both the acid andiron oxide produced are usable as such in steel plants. This entirelyobviates the problem of disposing of spent liquor and improves theoverall economy of the operation. The addition agents are likewiserecovered in their original form so there is no cost for materials used,once the method has been instituted.

Although I have disclosed herein the preferred embodiment of myinvention, I intend to cover as well any change of modification thereinwhich may be made without departing from the spirit and scope of theinvention.

I claim:

1. In a method of recovering spe'nt hydrochloric-acid pickle liquor, thesteps including introducing ammonia and oxygen into the liquor therebyto convert it to a complex ferroso-ferric hydrated oxide and an aqueoussolution of ammonium chloride, collecting the oxide and reacting thechloride solution with ammonium bisulphate at a temperature of from 80to 124 C. to produce a References Cited in the file of this patent mixedsolution of ammonium sulphate and hydrochloric UN ED TA acid, thenboiling oif the hydrogen chloride and crystal- IT S TES PATENTS lizingthe sulphate from the last mentioned solution. 2'529'874 Hoak 1950 2. Ina method as defined in claim 1 characterized by 5 OTHER REFERENCESheating the ammonium sulphate to decompose it into ammonia and ammoniumbisulphate, then using these decomposition products in the treatment ofmore spent pickle liquor.

Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 2, Longmans, Green & Co., New York, N. Y., 1922, page 164.

1. IN A METHOD OF RECOVERING SPENT HYDROCHLORIC-ACID PICKLE LIQUOR, THESTEPS INCLUDING INTRODUCING AMMONIA AND OXYGEN INTO THE LIQUOR THEREBYTO CONVERT IT TO A COMPLEX FERROSO-FERRIC HYDRATED OXIDE AND AN AQUEOUSSOLUTION OF AMMONIUM CHLORIDE, COLLECTING THE OXIDE AND REACTING THECHLORIDE SOLUTION WITH AMMONIUM BISULPHATE AT A TEMPERATURE OF FROM 80TO 124*C. TO PRODUCE A MIXED SOLUTION OF AMMONIUM SULPHATE ANDHYDROCHLORIC